The population on Obi Island, Indonesia, may represent a separate species. There is also a distinct population on the Atherton Tableland, Australia that may represent a separate species (previously described as Hydromys longmani) (K. Aplin and K. Helgen pers. comm.).

Justification:
Listed as Least Concern in view of its wide distribution, presumed large population, and because it is unlikely to be declining at nearly the rate required to qualify for listing in a threatened category.

This species is present on Obi Island in the Moluccan Islands of Indonesia, the Kai Islands (Indonesia), the Aru Islands (Indonesia), the islands of Biak-Supiori and Yapen (Indonesia), it is found over much of the island of New Guinea (Indonesia and Papua New Guinea), on the D’Entrecasteaux Islands and the Trobriand Islands (Papua New Guinea), and ranges through parts of northern, eastern, south-eastern and south-western Australia, including the island of Tasmania and a number of offshore islands (e.g., Bernier Island, Western Australia). It ranges from sea level to 1,900 m asl.

This species is associated with a wide variety of permanent aquatic habitats. It can be found in most types of freshwater habitats, including artificially irrigated sites, and can also occur in mangrove and estuarine areas (Flannery 1995a,b; Olsen 2008). Animals nest in bankside tunnels or logs, and while most food is taken from the water, they may forage in riparian vegetation (Olsen 2008). Females may annually have up to five litters (usually one or two) of three or four young (Olsen 2008).

There are no major threats to this species. In New Guinea, some populations are locally threatened by aquatic pollution resulting from mining activities. In south-western Western Australia, populations have declined likely due to increased salinity from clearing in agricultural areas. Extinction in the Montebello Islands (Western Australia) was probably due to a high density of introduced black rats (Rattus rattus) and cats.